The invention relates to mechanisms for mechanical movements, but more particularly, the invention relates to an actuator with reciprocating motion to or from alternating rotary motion.
Several types of mechanisms are available for converting rotary motion to linear motion or linear motion to rotary motion. As examples, such mechanisms include racks and pinions, cams, cranks, and hydraulics using piston-cylinder type combinations. Inherent friction of such mechanisms affect response and efficiency while also introducing associated undesirable characteristics such as noise and the requirement for lubrication.
Examples of alternating rotary to reciprocating type actuators that appear to overcome the drawbacks of friction, poor efficiency, requirement for lubrication, and noise are shown in U.S. Pat. 3,864,983 and U.S. patent application Ser. No. 335,981. These actuators are characterized by at least two coaxially arranged disc type members that are interconnected along their rims by a plurality of similarly oriented links formed of cords. One of the disc members is permitted to rotate about and reciprocate longitudinally along an axis in relation to the other disc member. Relative rotation of one disc member in one direction tensions the cords pulling the disc members together and shortening the axial spacing between the disc members. Rotation in the opposite direction decreases cord tension and increases the axial spacing between the disc members. While such actuators overcome disadvantages of prior art actuators, they also introduce their own problems such as attachment of the cords to the disc members without inflicting cord damage; unequal length cords that cannot substantially evenly share tensile loads; spacing the cords circumferentially along the rims of the disc members; and sharp bends in the cords that introduce flexural fatigue.